Conventionally, in a vehicle propelled by an electric motor, such a vibration suppression control system is known for controlling a motor torque thereof in which a steady torque target is determined based on the various vehicle information, a first torque target is calculated by a feedforward calculation (hereinafter referred to as F/F operator or calculation), and a second torque target is calculated based on a feedback calculation (hereinafter, referred to as F/B operator or calculation), respectively. Then, by addition of the first torque target and the second torque target, a motor torque command is obtained for controlling the motor torque (see for example Japanese Laid-Open Patent Application, No. 2003-9566).
However, in the conventional vibration suppression or damping control system for a vehicle using an electric motor, in any running or travelling scene, the first torque target (i.e., F/F torque) and the second torque target (i.e., F/B torque) are calculated using a model Gp(s) defining a transfer characteristic between a vehicle torque input and motor rotation speed. Therefore, there is a problem in such driving scenes that, where torsional vibration of the drive system hardly generates, the F/F and F/B calculations malfunction to cause unexpected vibration or shock.
For example, in such running scenes with the torque transmission being interrupted where a tire or wheel spins at drive force slip, or, a clutch disposed in a drive system or driveline is slipping or released, etc., torsional vibration hardly occurs in response to the change in motor torque. In these running scenes, since the transfer characteristic between the vehicle torque input and motor rotation speed is greatly different from the previously assumed model Gp(s), the F/F and F/B calculations using the model Gp(s) causes malfunctioning.